Nanofibrous Membranes Applicable in Lithium Ion Batteries

Seyedeh Nooshin Banitaba1; Dariush Semnani1*

Department of Textile Engineering, Isfahan University of Technology, Isfahan, Iran

*Correspondence to: Dariush Semnani, Department of Textile Engineering, Isfahan University of Technology, Isfahan,

Iran.

Tel: +98 31 3391 5006; Fax: +98 31 3391 2444; Email: d_semnani@cc.iut.ac.ir

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Abstract

Thischapteraimstofocusonthekeyroleoftheelectrospunnanofibersin the recent progressions for themodification of the lithium ion battery’scharacteristics. The use of nanostructured materials as various components (including cathode, anode, separator and electrolyte) of the lithium secondary batteriescanpotentiatetheirvariousfeatures.Thedevelopmentoftheelec-trospunelectrodesgives thepossibilityfor thepreparationofhighcapacitybatterieswithanexcellentcyclestability.Inaddition,fabricationofseparatorsthroughelectrospinningmethodcan lead to theelectrospunseparatorswithhigherelectrolyteuptakeandproperionicconductivity.Furthermore,nanofi-brousmembraneshavethepotentialforuseassolid-stateelectrolytesinlith-iumionbatteries.Theabilityofapplyingnanofibersinvariouscomponentsofthelithiumionbatteriesispromisingforthefabricationofall-solid-state,flexibleandlightweightnanofibrousbatteries.

1. Introduction

Energyhasalwaysbeenacrucialaspectofhumanlife.Savingandconvertingenergyplaysakeyroleinmankindsurvival.Nowadays,ithasbeenshownanincreasedinterestandneedforthedevelopmentofportableelectricalsources.Thesepowersourcesareconsideredasoneofthemostsignificantpartsinawidevarietyofapplicationsincludingnotebooks,mobile

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phones,electricalvehicles,medicaltools,satellitesandmanymore.Abatterycomprisesofoneormoreelectrochemicalcellswhichareconnectedtoeachotherinseriesorparallel.Theelectrochemical cell is consisted of a negative electrode (anode), a positive electrode (cath-ode),aseparatorandanelectrolytesolution.Inbatteries,oxidation-reduction(redox)reactionsoccurring in the electrodes, lead to the conversion of the chemical energy to the electrical en-ergy [1,2].

Ingeneral,batteriesaredividedintotwocategoriesincludingnon-rechargeablebatter-ies(primarybatteries)andchargeablebatteries(secondarybatteries).Theredoxreactionisnotreversibleinprimarybatteries.So,thedischargeprocesscanbelastedtillcompleteconsump-tionsofallchemicalcompounds.However,theredoxreactionisabletoberestoredbyapply-ingapotentialbetween twoelectrodes in secondarybatteries.Lead-acid,Nickle-cadmium,Nickle-metalhybridandlithiumion(Li-ion)batteriesareofthecommonsecondarybatteries.Li-ionbatteriesarethemostpromisingchargeablebatteriesduetothehighestenergydensityalongwiththelightestweightandthesmallestsizebetweenthementionedsecondarybatteries[1,2].

Li-ion batteries are also comprised of the anode, the cathode, the separator and theelectrolyte solution (Figure 1).Lithiumatomisthelightestweightmetal.Itcaneasilyloseitselectron and produce a lithium ion. The electron and the lithium ion move quickly due to the smallsizeandlowmassdensity.WhentheLi-ionbatteryisfullycharged,thelithiumatomsareplacedintheanode.Aslithiumatomstendtobeintheformoflithiumions, losetheirelectrons.Theproducedlithiumionsdesiretomovetowardsthecathodeduetoconcentrationgradient.However,thismigrationispulledinbytheattractionforcebetweentheLiionsandtheelectrons.Whenanelectricaltoolsuchasalamporalaptopisconnectedbetweentwoelectrodes, electrons and lithium ions are transferred to cathode through the cord and electro-lyte,respectively.ThedischargeprocesscanbecontinueduntiltheconsumptionofallLiions.The chemical reactions in the anode and cathode electrodes, during the discharge process is giveninequation1and2,respectively.Inordertorechargethebattery,itissufficienttoapplyahigherpotentialtothebattery[1,2].

LiC6 →C6 + Li+ + e- (1)

MOx+ Li+ e- → LiMOx (2)

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Figure 1:Schematicallyillustrationoflithiumionbatteries.

ThecharacteristicsoftheLi-ionbatteriessuchaspotential,capacityandenergydensitydepend on the ingredient features of the electrodes. In addition, safety and lifetimeof thebatteries are linkedwith the electrolyte and the electrolyte-electrode interface.Besides therawmaterialpropertiesofthebattery’scomponents,thesynthesisprocessplaysacrucialroleonbatteryperformance.Recently,researchershaveshownanincreasedinterestinapplyingelectrospun nanofibrousmembranes as components of the Li-ion batteries to enhance thementionedproperties[1,2].Thischaptersummarizestherecentresearchprogressestowardsthefabricationofthenanofibrousanode,cathode,separatorandelectrolyte.

2. Electrospun Nanofibers as Anode

TheelectrochemicalbehavioroftheLi-ionbatteriesisinfluencedbythechemicalandphysicalpropertiesof theanode.Highenergydensity , coulombefficiency and reversiblecapacityarecharacteristicsoftheidealanode.Since1991,carbon-basedmaterialshavebeenthebestchoiceastheanode.Highelectronicconductivity,longcyclelifeandlowcostareofotheradvantagesofthecarbon-basedmaterials.Inthemostcommercialbatteries,theanodesare made of graphite (capacity~300 mAh.g-1&energydensity~1-10Wh.kg-1) due to easily insertion of Li ions into the interspace between carbon layers during charging process.Agrowingbodyofliteratureshasfocusedonsilicon-basedanodeswhichshowedhighspecificcapacity around 3580 mAh.g-1.Alloyanodes(e.g.Li4Ti5O12)havealsoattractedaconsiderableattentionduetotheirhighspecificcapacity(400-2300mAh.g-1).However,thelargevolumetricchange (~400%) during charging-discharging processes limited the practical applications of siliconeandalloyanodes.Moreover,transitionmetaloxidesrevealappropriatecapacityrate(600-1000 mAh.g-1).Although, poor coulomb efficiency is amajor drawback of themetaloxideanodes[2-5].

Ithasconclusivelybeendemonstratedthatnano-sizedmaterialshavemoreaffinityfortheattractionof theLi ions resulting fromhighspecificsurfaceareaof thenanomaterials.The stronger adsorption ofLi ions enhances electrode activity and boosts capacity rate inthe anode terminal. In addition, diffusion length of theLi ions is decreased in nano-sized

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materialswhichleadstotheimprovementofthechargetransfer.However,therearecertaindrawbacksassociatedwiththeuseofthenanostructuredanodes.Highlyporousstructureofthenanostructuredanodescausesreductionofvolumetriccapacity.Moreover,lowproductionrate and high cost are of other limitations [3,6].

Nano-sized anodes have been synthesized through different methods such aschemicalvapordeposition,self-assembly,solutiongrowth,electrospinningandmanymore.Electrospinningasasimpleandcosteffectiveroute,providesapossibilityforthefabricationofnanostructureswithtunablecharacteristics[3,6].Todatecarbonnanofibers(CNFs)havebeen prepared from various electrospun sources for applying as anode inLi-ion batteries.Kim et al. [7] reported a high capacity rate of 450 mAh.g-1 at 0.3 A.g-1fortheCNFelectrode,obtainedfromelectrospunpolyacrylonitrile(PAN).However,theas-fabricatedCNFelectrodeshowed poor cycle stability. In 2010, Ji et al. [8] presented superior cycle life and higherstorage capacity (556 mAh.g-1 at 0.05 A.g-1) forCNF electrode prepared fromelectrospunPAN/polypyrrolenanofibers.Taoet al. [6]usedwastewalnut shells for the fabricationofCNFswhichpresented200mAh.g-1 at 0.1 A.g-1.Poly(vinylidenefluoride)[9],polyimide[10],polyvinylalcohol[11]andpolyvinylpyrrolidone[12]havealsobeenreportedassourcesforthefabricationofCNFelectrodes.

Jietal.[13]examinedthatthestoragecapacitycanbeimprovedto604mAh.g-1 at 0.05 A.g-1 byintroductionofFe2O3nanoparticlestotheelectrospunCNFs.Inaddition,incorporationofSnnanoparticlestotheelectrospunCNFsshowedenhancementofthewholeelectrochemicalperformancesoftheanodeelectrodeapplicableinLi-ionbatteries[14].Studiesalsohaveshownthatinsertionofmanganeseoxide[15],titaniumdioxide[16],tindioxide[17]andmagnetite[18]nanoparticlesintotheCNFmembranescanboosttheelectrochemicalcharacteristicsofthe anode electrode.

LargevolumetricchangeduringLiinsertionandextractioninthesilicone-basedanodeshavebeenaseriouslimitationformanyearlierstudies.Thisvolumechangeleadstothepoormechanicalpropertiesandlowcyclelife.Studieshaveshownthatsilicone-loadednanotubesandnanofibersprovideaspecificstructurewhichisabletoabsorbtheappliedstressandpreventthecracks[19,20].Xueandcoworkers[21]reportedenhancementofthecyclestabilityfortheCNFanodeloadedwithSi/Cnanoparticles.Hwangetal.[22]demonstratedpropercyclingdurabilityandhighstoragecapacityof721mAh.g-1 foracore-shellnanofibrousanode (SiasthecoreandCastheshell).Wangetal.[23]showedlowchangesinthemorphologyoftheanodepreparedby theelectrospunSi/Cnanofibers. Inaddition,porousC/Sicompositenanofibershasshownlongcyclelifewithahighcapacityrateof1100mAh.g-1 at 0.2 A.g-1 [24].

Severalstudiesthusfarhavelinkedalloyssuchassilicon,tinandantimony-basedalloys

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withCNFstoimproveelectrochemicalperformancesoftheanode.Jangetal.[4]reportedastable structurewithhighcapacity storageof560mAh.g-1 for theCNFsfilledwithCo-Snalloy.AnenhancementinthemechanicalstabilityalongwithpropercapacityratewasalsoillustratedbyincorporationofCu-Sn[25],Sn-Sb[26],Ni-Sn[27],Ag-Fe-Sn[28]andmanymorealloysintotheCNFanodes.

3. Nanofirbous Membanes as Cathode

CathodematerialinLi-ionbatteriesdependsontheappliedanodeintheelectrochemicalcell.WhenalithiummetalisusedasanodeinLi-ionbatteries,itisnotneededtoapplyalithiatedcathode.However,itisessentialtoutilizelithiatedcathodewhentheanodeiscarbon-based.Cathodematerialsignificantlyinfluencesthebatteryperformance.TransitionmetaloxidesandphosphatesarethemainchoicesasthecathodeofLi-ionbatteries.In1980,Goodenoughetal.introducedLithiumcobaltoxide(LiCoO2)ascathodewhichhasbeenthemostsuccessfulcathodeincommercialLi-ionbatteries.However,lowstabilityandhighcapacityfadinghavehindereditsfurtherapplications.OlivineLiMPO4(M=Fe,Mn,NiandCo)providesappropriateelectrochemical characteristics includingproper cycle life and specific capacity.Generally,olivinecathodematerialspresentedlowcyclestabilityandcapacityrate [29-32].

Lithiumlayeredmetalandvanadiumoxidesarethemainpromisingclassesofcathodematerials. Layered oxides have shown more stability in various temperatures and highercapacitystorage.Li-richedmetaloxides(xLi2MnO3.(1−x)LiMO2(M=Ni,Co,Mn))andNCM(LiNixCoyMnzO2 (x+y+z=1))areclassifiedaslayeredoxides.Notably,poorcyclelifeandthecapacitylossarethemaindrawbacksofthelayeredmetaloxidesascathodeofLi-ionbatterieswhichneedtobeimproved.LithiatedvanadiumoxidesincludingLiVO3,LiV2O5,Li1+xV3O8 and many more, have illustrated a high discharge capacity rate ( ).However,migrationof vanadium ions leads to the high capacity fading [29-32].

Much of the current literatures on the cathode of theLi ion batteries pay particularattention to the synthesis of the nano structure cathodes. Morphological and electrochemical featuresof theelectrospunLiCoO2 [29-32],OlivineLiMPO4,Lithiumlayeredmetaloxides[33]andlithiatedvanadiumoxides[34,35]havebeenwidelystudied.ReductionoftheLiionpath lengthandso increasing thediffusion rate improvecycle lifeand theelectrochemicalperformance [31].Chenet al. [30]preparednanofibrousLiCoO2 byannealingof thePVP/LiCoO2 at700°Cfor12hours.LiuandTaya[32]fabricatednanofibrousLiCoO2 membranesbyelectrospinningoflithiumacetate/cobaltacetate/PVPsolutions.TheresultedelectrospunLiCoO2 showedhigherstoragecapacitycomparedwiththecommonLiCoO2 cathodes. Zhang andcoworkers[2]suggestedelectrospunLiFePO4/CcathodeforcompensationoflowelectricalconductivityofLiFePO4andsoimprovementofthecyclestability.TheLiMn2O4poroushollownanofiberspresentedastablecyclingbehaviorover400cycles[36].Inaddition,electrospun

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LiNi1/3Co1/3Mn1/3O2 andLiNi3/8Co1/4Mn3/8O2 nanofibers have shown a proper dischargecapacity ( 170 mAh.g-1)andretainedthecapacityabout90%after50cycles[33].Yuetal.[34]suggestedmesoporousV2O5nanofiberswiththestoragecapacityof370mAh.g

-1 and high cyclestabilityascathodematerial.Anetal.[37]fabricatedcarbonencapsulatedhollowporousnanofibersofV2O5ascathodeofLiionbatterieswhichshowedhighspecificcapacitywithanexcellentcyclingstability.

4. Electrospun Separators

Separatorisathinandporousmembrane,locatedbetweentheanodeandthecathode,whichpreventstheelectroniccontactoftwoelectrodes.Inaddition,separatorsmaintaintheliquid electrolyte and enable migration of Li ions between two electrodes during charge-dischargeprocess.Separatorsplayakeyroleinthebatteryperformance.Energydensity,cyclestabilityandsafetyofthebatteryareinfluencedbytheseparator’sfeatures.Anidealseparatorshouldoffersufficientchemical,electrochemical,dimensionalandmechanicalstabilities,highelectrolyteuptake(EU%),appropriateionconductivity(1-10mS.cm-1),lowthickness(20-25µm),highporosity(ɛ>60%),smallporesizes(˂1µm)andsoon.Inthemostcommercialbatteries,microporouspolyolefinmembranes(e.g.polyethylene(PE),polypropylene(PP)andtheirblends)areusedasseparator.Polyolefinmembranesprovideappropriatemechanicaland chemical stability against the electrodes and the electrolyte.However, lowwettability(EU~50%)of themembranesresultingfromlowporosity(~40%) leads to thepoor ionicconductivity(0.8mS.cm-1)andreducedcyclestabilityofthebattery.Inaddition,largeporesizesinthepolyolefinmatsmaycausepenetrationofelectrodecomponentsandinternalshortcircuits.Notably,preparationofapolyolefinmatwithsmallporesizesseemstobeimpossibleconsideringtheaveragediameterofthepolyolefinfibers(~1μm)[38,39].

Tomodifythefeaturesofthepolymermembranes,severalpolymershavebeenappliedtosynthesisof thepolymermembranessuchasPVDF,PANandpolymethylmethacrylate(PMMA).NumerousstudieshaveshownthatthemembraneelectrolytesbasedonthePVDF(ɛ~57%andEU~152%andσ~1.5mS.cm-1)andPAN(EU~70%andσ~1.5mS.cm-1) provideproperelectrochemicalstability,highelectrolyteuptakeandgoodionicconductivityat room temperature. Although, mechanical strength fading and reduction of ionic conductivity uponlongstorageareofundesirableeffectsofthePVDFandPANmembranes,respectively[40,41].

Non-woven fabrics and inorganic composites are two promising classes of theseparators.Non-wovenfabricmatsarecommonlymadefrombonding(physical,chemicalormechanicalbonding)ofvariousnaturalor syntheticfibers includingcelluloses,polyamide,polytetrafluoroethylene, PVDF, etc. Non-woven fabric mats provide a porous structurecontaininglargeporesizes.Thisformofseparatorsaretypicallyappliedasasupportmembrane

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for the gel electrolytes. Inorganic composite separators are referred to porousmembranesformedbybondingof theceramicparticles suchasalumina, silicaandzirconia.Excellentwettabilityandthermalstabilityarethemaincharacteristicsoftheinorganiccompositemats.However,handlingofsuchseparatorsisstillachallengefortheassemblyofthebatteryduetopoormechanicalstrengthoftheceramicmats.Inaddition,tuningthethicknessoftheinorganiccompositesisproblematicbecauseoftheaffinityoftheceramicparticlestoaggregation[38,42].

Oneofthemostsignificantcurrentdiscussionsinmodificationoftheseparatorproperties,is fabrication of nanofibrous polymermembranes through electrospinningmethod.Highlyporousstructure (~90%)of theelectrospunmembranesprovidesproperpermeabilityandwettabilitywithsuitablepathwaysforthemigrationofLiionswhichleadtolithiumsecondarybatterieswithhigherpowerdensityandratecapability.ThemorphologicalandelectrochemicalcharacteristicsofthePVDF,PAN,polyethyleneterephthalate(PET)and(PMMA)nanofibershavebeenwidelystudiedaspromisingseparatorsinLiionbatteries.Theas-spunmembranespresentedhighaffinityfortheabsorptionofliquidelectrolytes.Inaddition,compatibilitywiththeelectrodes,excellentthermalandelectrochemicalfeaturesandtunablemorphologyareofotherdesirablepropertiesofthesenanofibrousseparators.Chaoandcoworkers[43]showedthattheelectrospunPANcouldenhancetheporosityandcyclestabilityupto76%and85%,respectively.Gopalanetal.[44]reportedthatelectrospunPVDF-PANnanofiberscouldreveal84%porosity, 300%electrolyte uptakewith a high conductivity of 7.8mS.cm-1 at room temperature.Inaddition,electrospunmembraneofPVdF-HFP/PMMAhasillustrated377%electrolyte uptakewith ionic conductivity of 2mS.cm-1 at ambient temperature.YanilmazandZhange[45]alsoshowedthepotentialof theelectrospunPMMA/PANnanofibers(ɛ~73%, EU ~ 370% and σ ~ 3.2mS.cm-1) as separator of the Li ion batteries.Moreover,recent evidences suggest that incorporation of nanoparticles into the nanofibers or coatingthemembraneswiththenanoparticlesincludinggrapheneoxide[46],silica[47-49],Alumina[50,51] and many more, can furtherly improve mechanical and electrochemical characteristics of the separators.

5. Nanofibrous Electrolytes

In general, electrolytes are used in a liquid form in commercial lithium secondarybatteries.Liquidelectrolytescontainorganicsolventsandlithiumsalts.ThepresenceoftheflammableandexplosivesolventsinthestructureoftheLiionbatteriesisabigconcernwhichthreatens the safetyof thesebatteries. Inaddition, ametal cover is essential for sealingoftheLiionbatteriesleadstothefabricationofinflexibleandheavystructures.Solidpolymerelectrolytes (SPEs) are an ideal choice for the fabricationof lightweight,flexible and safebatteries.However,lowionicconductivity( )oftheSPEslimitedtheirpracticalapplications.Aschematic illustrationof theLi ionbatterycomprising theSPEisshownin

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Figure 2.Asitisapparent,theSPEactsasboththeelectrolyteandtheseparator.Infact,SPEssimultaneouslytransfertheLiionsandpreventthephysicalcontactofthetwopositiveandnegative electrodes [38].

SPEsarecommonlysynthesizedthroughdispersionofalithiumsaltinapolymermatrixbyusingahotpressingorasolutioncastingmethod.Numerouspolymers(e.g.PVDF,PAN,polyvinylalcohol(PVA),polyethyleneoxide(PEO))havebeenevaluatedasthepolymermatrixintheSPEs.Amongseveralpolymers,PEOhasbeenexaminedasthemostappropriatematrixduetotheabilityforthesolvationofvarioussaltsandadditives.Inaddition,PEOisanabundantandacost-effectivepolymer.Lithiumtetrafluoroborate(LiBF4),lithiumperchlorate(LiClO4) andlithiumhexafluorophosphate(LiPF6)areofcommonlithiumsalts.InSPEs,lithiumionsmigratethroughlocalmovementsofthepolymerchains.Inpolymerstructures,themobilityofthepolymerchainsoccurinamorphousregionsandaboveglasstransitiontemperature(Tg).So, the reductionsofcrystalline regionsandTgof thepolymermatrixcausean incrementin the ionic conductivityof theSPEsat ambient temperature.Numerouseffortshavebeendevoted toenhance ionicconductivityof theSPEs.Synthesisofsingle ionconductingandpolymer-in-salt electrolytes, preparationof copolymers andadditionofvariousplasticizersandfillersareseveralattemptshavebeenmadefortheenhancementoftheionconductivityoftheSPEs.Asanexample,withintroductionofplasticizersintotheSPEs,plasticizermoleculespenetratebetweenthepolymerchains,weakentheirinteractions,increasemovementsofthepolymerchainsandsoenhancetheionicconductivity.Inaddition,incorporationoffillerssuchasinertandactiveceramicfillers(titaniumdioxide(TiO2),aluminumoxide(Al2O3), silicon dioxide(SiO2),etc.)causesformationofmoreamorphousphasesinpolymerstructureswhichleads to the increase of the ionic conductivity [52,53].

Vignaroobanandcoworkers[54]presentedthattheionicconductivityofaPEO/LiTFelectrolytecanbeimprovedupto0.049mS.cm-1bytheadditionof10wt.%TiO2. Moreover, theobtainedionicconductivitycanbefurtherlyenhancedto0.16mS.cm-1byintroductionof50wt.%ECintotheas-preparedelectrolyte.Johanetal.[55]illustratedthationicconductivityof a PEO/LiCF3SO3/EC electrolyte can be improved from 0.3mS.cm

-1 to 0.8mS.cm-1 by

Figure 2: SchematicillustrationoftheLiionbatterywiththe(a)solidpolymerelectrolyteand(b)nanofibrouspolymer electrolyte.

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theadditionof20wt.%Al2O3 nanoparticles.Embedding10wt.%TiO2 nanoparticles into the PVDF/LiClO4 polymermembranes yielded ionic conductivity of 0.7mS.cm

-1 at room temperature [56].

Recently,literatureshaveemergedthatofferapplyingelectrospuncrystalstructuresasfillerinSPEs.Besidetheincrementofamorphousphases,electrospunfillerscreatepathwaysfortransportationoftheLiionswhichenhancetheionicconductivity.Liuetal.[57]reportedahighionicconductivityof0.24mS.cm-1forthePAN-LiClO4electrolyteincorporatedwith15wt.%Li0.33La0.557TiO3 electrospun nanowires.Tang et al. [58] also presented that ionicconductivityofthePAN-LiClO4 SPEcanbeimprovedto0.13mS.cm

-1withtheadditionofLi7La3Zr2O12nanowires.Anenhancement in the ionicconductivityof theSPEshasalsobeenpresentedbytheadditionofwellalignedLi0.33La0.557TiO3nanowires[59],polyanilinenanofibers[60],Li6.4La3Zr2Al0.2O12nanowires[61]andsoon.

ItisworthtonotethatamajorproblemwiththeSPEs,synthesizedthroughthesolutioncasting method, is phase separation and formation of crystal phases of lithium salts or crystal regions of lithium salt-PEO.Thementionedunwanted crystalline regions trapLi ions andthereforedecreasethefractionoffreeionswhichleadtothereductionoftheionicconductivity.In 2017, Freitag et al. [62] showed that electrospinning technique can also be an efficientmethodfor thefabricationofSPEs.TheelectrospunPEO/SN/LiBF4hasshownthehighestconductivityofabout0.2mS.cm-1 atambienttemperature.Inaddition,theresultsconfirmedtheabsenceof theunwantedcrystallinephases includingLiBF4or (PEO)3/LiBF4 in the as-spunelectrolytes.Inanotherattempt,theyshowedthepotentialoftheelectrospunmembranescontainingsodiumsaltsasthesolvent-freeelectrolyteinsodiumionbatteries[63].In2018,Walkeetal.[64]evaluatedtheeffectofLiTFSIsaltontheelectrochemicalbehaviorofthePEO/SNelectrospunelectrolytes.TheelectrospunPEO/SN/LiTFSIelectrolyteshowedthehighestconductivity of 0.28mS.cm-1 at room temperature,while theSPEwith the same chemicalcomposition, fabricated by solution casting method, illustrated ionic conductivity of 0.05mS.cm-1.Inaddition,Banitabaetal.[65]examinedtheconcentrationeffectsofthepolymer,saltandplasticizeronthecharacteristicsofthePEO/PC/LiClO4 electrospun electrolytes. The optimumelectrospunelectrolytehasshowntheionicconductivityof0.05mS.cm-1,about30timesgreaterthanthepolymerfilmelectrolytewithsimilarchemicalcomposition.Moreover,the impact of the TiO2nanoparticlesonthevariouspropertiesofthePEO/PC-EC/LiClO4 has alsobeeninvestigated[66].

6. Concluding Remarks

Insummary,numerousresearcheshaveshownthepotentialoftheelectrospunnanofibersforbeingappliedasvariouscomponentsincludingelectrodes,separatorsandelectrolytesofthelithiumionbatteries.ElectrospunnanofibersprovideshorterpathwaysfordiffusionoftheLi

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ionsinthenegativeandpositiveelectrodeswhichcauseenhancementofthecapacitystorageandchargetransfer.Applyingtheelectrospinningmethodforthefabricationofnanofibrousseparatorsimprovesporosity,electrolyteuptakeandionconductivitywhicharecrucialkeysforthedevelopmentofLiionbatteries.Inaddition,incorporationofelectrospunnanowiresinsteadofnanoparticlesasfillerintotheSPEssignificantlyimprovestheirionconductivity.Moreover,electrospunmembranesproposemoreionicconductivitycomparedwiththeSPEsassociatedwiththeiruniquestructures.Theoutstandingstructureoftheelectrospunnanofiberspotentiatethepossibilityofthefabricationoflightweightandflexiblenanofibrousbatterieswhichareapplicableinawidevarietyofprogressiveapplications.

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